Why do we need self-referential structure?

[sathishc58]

Hi All,

We know what is self-referential structure and it is widely used in creating data structure (for ex: linked-list)

struct xxx
{
int a;
struct xxx *ptr;
}

Why should I declare "ptr" to be of the same type. Cannot I declare "ptr" as "int" or "void" as it is going to store only the address.

I searched net, but most of the pages explain self-referential structure but I could not find the reason.

Thanks & Regards
Sathish Kumar

[Banfa]

You declare pointer as the type it will be pointing to, that is struct xxx. Since the C (and C++) standard does not guarantee that you can safely cast a pointer to a type to anything other than void and that you can only safely cast a void pointer back to a pointer to the type it originally pointed to your only safe options when creating a linked list would be struct xxx* and void*.

If you used void* you would have to put a cast into the code everywhere you used it which would make the code extremely messy and unmaintainable. So of the 2 safe options it makes sense to struct xxx* in order to keep the code clean.

[donbock]

"Why should I declare "ptr" to be of the same type. Cannot I declare "ptr" as "int" or "void" as it is going to store only the address."

The ptr field is a pointer to another instance of the structure. With enough engenuity you could manage to coerce a different data type to act like a pointer-to-structure, but why go through the effort (and risk)?